Method of embedding electrical high voltage apparatus



May 26, 1959 A. IMHOF 2,387,729

METHOD OF EMBEDDING ELECTRICAL HIGH VOLTAGE APPARATUS Filed June 15.1954 rag-.2,

United States Patent METHOD OF EMBEDDING ELECTRICAL HIGH VOLTAGEAPPARATUS Alfred Imhof, Zurich, Switzerland Application June 15, 1954,Serial No. 436,866

Claims priority, application Switzerland June 18, 1953 2 Claims. (Cl.18-59) The present invention relates to high voltage apparatus and to amethod for manufacturing same.

It is an object of the present invention to avoid the drawbacks anddeficiencies of high voltage apparatus, particularly if the same haveinsulating parts consisting of a casting resin.

It is another object of the present invention to avoid the internalmechanical stresses due to contractions during the hardening,contractions and extensions occurring at changing temperatures, and/ orfaulty casting.

It is a further object of the present invention to avoid the drawbacksdue to inaccessibility of embedded parts.

It is still another object of the present invention to avoid thedrawbacks due to the necessity of the repair or replacement of entireapparatuses in case of defects during the operation or the testing ofthe apparatus.

According to the present invention, these difliculties and deficienciesare avoided in a simple manner by manufacturing the entire insulatingparts of high voltage ap paratuses and the like from parts, preferablyconsisting of casting resin, which may be assembled like bricks, andfilling the joints remaining between the insulating structural partswith an easily deformable insulating material having high-classdielectric properties.

For such easily deformable materials are suitable materials being liquidat normal temperature, ointments, paste-like materials, mixtures of suchmaterials with mineral or organic powders, easily deformable solids,particularly in shape of flexible foils wetted by liquid or pastymaterials, rubber-like materials, also in combination with solventsrendering the surface thereof soft and sticky, porous materialsimpregnated with liquid dielectries, gases and mixtures thereof having ahigh dielectric strength such as compressed air, compressed nitrogen,compressed carbon dioxide, gaseous halogens, etc.

The subdivision of the entire insulation into individual insulatingparts may be arbitrary or governed, for instance, by the nature and formof the part to be embedded, for instance a metal, or by the mechanical,electric, and dielectric requirements, etc. Apparatuses of any size maybe insulated according to the present invention.

Particular advantages of the invention reside in the fact that thejoints are easily formed when the insulating parts are manufactured bycasting; for instance, the joints may be formed in a very simple mannerby arranging separating Walls in advance and removing the same after thecasting so that even complicated joints can be achieved without afinishing operation.

If the joints are narrow and if liquid dielectrics are only used asimpregnating materials of porous foils or as Wetting agents of flexiblesolid dielectrics, the quantity of the liquid dielectric is relativelysmall, thus reducing the danger of fire and rendering feasible the useof, for instance, expensive liquid materials which have more valuableproperties such as of being not easily inflammable,

2,887,729 Patented May 26, 1959 of being incombustible, or of a widelyuniform viscosity over a large range of temperatures, a small surfacetension particularly coupled with the property of a good wettening, avary high electric strength, a low loss factor, a high chemicalstability, slow soot formation, etc.

Materials having all these and further advantageous properties are, forinstance, silicon oils, certain fluoroethers, certain fluoro-t-amines,chloro-phenyl-indane, chloro-diphenyls. The halogen compounds mentionedhereinabove have, i.e., the particular advantages of incombustibility,partly also non-sootability, high electric strength, compatibility withthe solid insulating materials used according to the invention, goodwettability, high heat and cold resistance.

Silicon oils are furthermore advantageous because the viscosity thereofremains the same within wide limits of temperature; also those areusable, which for instance remain liquid from -60 C. to 200 C.Furthermore, they are Water-repellant. Also very viscous silicon oilsare to be taken into consideration since they render easy anty sealingand have particularly good dielectric propfil 16S. Fluoro-t-amines andfluoro-ethers are advantageous if it is a question of a very lowdielectric constant, somewhat smaller than 2, Whereas theehloro-diphenyls have a particularly high dielectric constant and arerelatively inexpensive.

instead of chloro-diphenyls, the chloro-phenyl-indanes with propertiesvery similar to those of the chloro-diphenyls are advantageous and aredistinguished from the latter by the greater chemical stability thereof,particularly at higher temperatures.

Fluoro-ethers, fluoro-t-amines, and fluoro-indanes are moreover verystable under changes of temperatures, have a very good wettability, anda high dielectric strength. In this respect they are superior to, forinstance, mineral oils; but particularly they are entirelyincombustible.

As insulating materials for the solid structural elements areparticularly suitable the casting resins and among these particularlythe embedding resins hardening from the direct initial materials thereofby a poly-reaction such as a polymerization or poly-addition without thesplitting off of volatile components. These materials adapt themselvesso Well during and after casting to the metal parts under voltage or themetallic or insulating covers, etc. that small joint spaces result.

Preferably the joints are designed in such manner that the electricfield lines are normal or at least approximately normal to the joints.

In order to seal the joints, the latter may be packed by a foil of solidmaterial which is wetted on both sides with a liquid insulatingmaterial. The liquid may be prevented from flowing out of the joints byutilizing for sealing purposes, for instance the marginal portions ofthe material filling the joints. A desired complete filling of the jointby the liquid may be obtained particularly by a reduction of the widthof the joints after the filling operation. In certain cases, the packingof the joint consists preferably of a porous foil, the marginal portionsof which are preferably non-porous. The porous portion is filled with adielectric liquid, the marginal portions serving as a sealing means.

In case of a cooling of the apparatus or apparatuses, for instance fordrawing off the heat generated by the copper losses, or dielectric orother losses, the joints may be connected with one another and thepreferably liquid filling material subjected to a circulation, forinstance by recooling the same in a cooling device The apparatuses orgroups of the same having a bricklike structure may be cast in one pieceand in one form.

The spaces of the joints are formed thereby as to position and formpreferably by walls arranged in the molding form preferably consistingof a material which does not adhere to the resin such as polyethylene orpolytetrafluoro-ethylene, so that they may be removed with great easeafter a hardening of the resin. However, the walls may consist insteadof a material such as metal sheet which is provided with a suitablecover or coating, for in stance of silicone fat.

Preferably also active parts of the apparatus are protected againstadhering to the resin bodies, for instance by coating the parts with amaterial preventing any adhesion, or by covering the parts with a foilwhich either prevents the adhesion by its own nature or does this afterbeing covered with a varnish or coating.

In cases when the apparatus should be provided with a metallic cover itis advisable to use the metal cover itself as a casting mold. Therequired joints between the walls of the casing and the resin body areautomatically formed by the contraction of the resin, particularly ifthe walls of the casing are provided on the inner side thereof with acoat preventing any adhesion.

Other objects and advantages of the present invention will become clearfrom the following detailed description thereof with reference to theaccompanying drawings showing, by way of example, some embodiments ofthe present invention. In the drawings:

Fig. 1 is a sectional elevation of a voltage transformer with insulatingparts according to one embodiment of the present invention;

Fig. 2 is a sectional elevation of a modified embodiment of the voltagetransformer shown in Fig. 1;

Fig. 3 is a sectional elevation of a current transformer according tothe present invention; and .Fig. 4 is a sectional elevation of theembodiment shown in Fig. 3 taken at right angles thereto.

Referring now to the drawings and first to Fig. 1, a voltagetransformer, one terminal of which is grounded, compi'isesa primarywinding 1 enclosing the secondary wind ing 2 which in turn is wound onthe magnetic iron core 3. Between the windings 1 and 2 an insulatingtube or pipe 4 is arranged which together with the solid insulatingparts mentioned hereinafter consists partly of porcelain, ceramics, orcasting resin. The primary winding 1 and part of the insulating pipe 4are enclosed by the insulating structural members 5 and 6 in acasing-like manner. Between these parts joints 7 are arranged which arefilled by a liquid insulating material. The conductor 8 serving as ahigh voltage lead-in is closely surrounded by an insulating member 20serving as a lead-in insulation. The ends of the pipe 4 are closelyconnected with the insulatinglparts 5 and 6, for instance by a cementconsisting of synthetic resin, or in case of the application of ceramicsor glass by a metal solder.

The voltage transformer shown in Fig. 2 differs from that shown in Fig.1 by a metal casing 9 containing the solid insulating members 5 and 6.

Referring now to Figs. 3 and 4 showing a current transformer, a primarywinding 10, is enclosed by a metallic mantle 11 continued by a stem 12serving as a guiding means for the leads (not shown) of the primaryWinding 10. The transformer is arranged in an insulating body 13consisting of casting resin and provided at its upper side with afunnel-shaped continuation 14. A condenser lead-in 15 is arranged to dipwith the lower end thereof into the continuation 14 and is separatedfrom the same by a conical joint 16 filled with an insulating liquid. Onits upper side, the joint 16 is sealed by means of a ring washer 17. Aniron core 18 is arranged within the central cross sectional part 21 andcarries the secondary winding 19 of the transformer. If desired, thecondenser lead-in may be protected by ceramic or porcelain screens (notshown) against rain and moisture, if the apparatus is intended foroutdoor use.

Having now particularly described the invention and the advantages anduses thereof in connection with voltage and current transformers, itwill be understood that it may be applied if desired, to other types ofapparatus such as dry rectifiers, enclosed bus bar systems, or anycombination of the same, and that the invention is not to be limited tothe details herein disclosed, otherwise than set forth in the appendedclaims.

I claim:

1. A method of enclosing a high voltage apparatus in an electricinsulation consisting of individual rigid insulating blocks formingjoint spaces between each other, said method comprising the steps ofplacing a high voltage apparatus into a mold, arranging removablepartitions at the spaces defining the joints of the insulation, castinga polymerizable resinous material in said mold, setting said resinousmaterial into blocks separated by said partitions, removing saidpartitions, and filling the spaces previously occupied by saidpartitions with a readily deformable insulating material.

2. A method as claimed in claim 1, comp-rising coating a metal moldforming the enclosure of the apparatus with a coating preventing thesticking of the casting material, and casting the resinous material intosaid coated metal mold.

References Cited in the file of this patent UNITED STATES PATENTS1,888,613 Apple Nov. 22, 1932 2,068,940 Wiseman Ian. 26, 1937 2,094,287Zimmerman et al Sept. 28, 1937 2,112,241 Hyde Mar. 29, 1938 2,216,010Hobart Sept. 24, 1940 2,262,831 Burleson Nov. 18, 1941 2,402,366 CamilliJune 18, 1946 2,489,891 Hull Nov. 29, 1949 FOREIGN PATENTS 679,220Germany Aug. 1, 1939 473,119 Italy July 12, 1952 OTHER REFERENCESPublication, Silicone Rubber Emerges as a Dielectric Material,Electrical Manufacturing, June 1950, pages 101-103, 200, 202. (Page 101relied on.) (Copy in Scientific Library and Div. 69 174-1107.)

